Vehicle Motion Control Device

ABSTRACT

There is provided a vehicle drive control system that feels less unnatural and that enables an improvement in safety performance. A vehicle motion control system capable of independently controlling a driving force and a braking force of four wheels comprises: a first mode (G-Vectoring control) in which substantially the same driving force and braking force are generated with respect to left and right wheels among the four wheels based on a longitudinal acceleration/deceleration control command that is coordinated with the vehicle&#39;s lateral motion; and a second mode (sideslip prevention control) in which different driving forces and braking forces are generated with respect to the left and right wheels among the four wheels based on a target yaw moment derived from the vehicle&#39;s sideslip information, wherein the first mode is selected when the target yaw moment is equal to or less than a pre-defined threshold, and the second mode is selected when the target yaw moment is greater than the threshold (FIG.  11 ).

TECHNICAL FIELD

The present invention relates to a vehicle motion control system capableof controlling the driving forces and braking forces of four wheels.

BACKGROUND ART

A command value for automatically performing acceleration/decelerationthat is coordinated with steering operations is disclosed, for example,in Non-Patent Document 1 ((Eq. 1)).

[ Eq .  1 ] G xc = - sgn  ( G y · y  )  C xy 1 + Ts   G . y  + Gx_DC ( Eq .  1 ) (  G . y = G y  _dot )

This is basically a simple control rule where lateral jerk G_(y) _(—)dot is multiplied by gain C_(xy), and a value to which a first-order lagis imparted is taken to be longitudinal acceleration/decelerationcontrol command G_(xc) (equivalent to target longitudinalacceleration/deceleration control command (G_(xt))). It is confirmed inNon-Patent Document 2 that an expert driver's coordinated controlstrategy for lateral and longitudinal motions may thus be partiallysimulated. G_(x) _(—) _(DC) in the equation above is a decelerationcomponent that is not coordinated with lateral motion. It is a term thatis required in cases where there is anticipatory deceleration when acorner is ahead or where there is a zone speed command. Further, the sgn(signum) term is a term provided so that the operation above may beattained with respect to both right corners and left corners.Specifically, an operation may be attained where deceleration isperformed at turn-in upon starting steering, deceleration is suspendedonce at steady turn (since lateral jerk becomes zero), and accelerationis performed upon starting to ease steering when exiting the corner.

When thus controlled, with respect to a diagram in which the horizontalaxis represents the longitudinal acceleration of a vehicle and thevertical axis the lateral acceleration of the vehicle, the combinedacceleration (denoted by G) of longitudinal acceleration and lateralacceleration is so oriented (vectored) as to transition in a curvedmanner with the passage of time. It is therefore called “G-Vectoringcontrol.”

In addition, with respect to a sideslip prevention system for improvingsafety performance at the critical driving region, it is reported inNon-Patent Document 3 that because it becomes unstable (divergent) whenvehicle behavior transitions to a region in a phase plane for vehiclesideslip angle β and vehicle sideslip angular speed (β_dot) that isapart from the origin and where the signs of β and β_dot are the same(the first and third quadrants), it is effective when used in thedetermination for activating the sideslip prevention system. It isdisclosed that the vehicle is stabilized by applying different brakehydraulic pressures on the left and right wheels based on sideslipinformation, generating decelerating forces that differ between the leftand the right, and generating a yaw moment in a direction in which thesideslip angle becomes smaller.

-   Non-Patent Document 1: M. Yamakado, M. Abe: Improvement of Vehicle    Agility and Stability by G-Vectoring Control, Proc. of    AVEC2008-080420.-   Non-Patent Document 2: M. Yamakado, M. Abe: Proposal of the    longitudinal driver model in coordination with vehicle lateral    motion based upon jerk information, Review of Automotive    Engineering, Vol. 29. No. 4. October 2008, P.533˜541.-   Non-Patent Document 3: S. Inagaki, I. Kushiro, M. Yamamoto: Analysis    on Vehicle Stability in Critical Cornering Using Phase-Plane Method,    Proc. of AVEC1994-9438411

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

It is indicated in Non-Patent Documents 1 and 2 that this control methodis extracted from brake and accelerator operations corresponding tosteer operations that an expert driver performs voluntarily, and thatthere is a possibility that it would not feel unnatural even if there isautomatic intervention from a normal region, and improvements in themechanical rationality, maneuverability, and stability of this controlmethod are presented as simulation results. This means that becauseacceleration/deceleration is controlled in a coordinated manner so thatthe behavior of the vehicle would respond appropriately to the driver'ssteering operation, it is consequently possible to prevent the sideslipangle of the vehicle from becoming large. In particular, it is effectivein reducing so-called “understeer” where the turning radius becomes toolarge relative to steering.

On the other hand, this control does not guarantee that, should thesideslip angle inadvertently become large for some reason, it will bereduced for certain. By way of example, if the vehicle lateral motionstabilizes while in a drifting state where the sideslip angle has becomelarge, lateral acceleration becomes constant, and lateral jerk becomeszero. As a result, the acceleration/deceleration control commandrepresented by (Eq. 1) becomes zero, and a stable state is entered whilethe vehicle is still drifting. Although stable mechanically, there is noguarantee that driving that does not feel unnatural to any driver isattained.

In addition, although the sideslip prevention system disclosed inNon-Patent Document 3 operates based on sideslip information, noguidance is provided with respect to operating from the normal regionwhere there is little or no sideslip. Further, from the perspective of“understeer” prevention, which is a forte of “G-Vectoring control,” itwould mean that the “sideslip prevention system” is such that a momentis introduced only after sideslip has occurred to some significantextent. Thus, control tends to be after the fact, requiring a largemoment to reduce understeer. As a result, there are concerns that theundersteer reducing effect would become smaller, while causing anunnatural feel due to excessive deceleration.

In addition, no consideration is given to the deceleration that occurswhen the sideslip prevention system generates a yaw moment. Thus, themoment to be generated is determined first, and the vehicle'sacceleration/deceleration is determined by the combined force of theleft and right braking forces. Given the above, it cannot be said thatacceleration/deceleration is coordinated with lateral motion.

An object of the present invention is to provide a vehicle drive controlsystem that reliably reduces sideslip in the critical driving region,feels less unnatural, and enables an improvement in safety performance.

Means for Solving the Problems

With a view to attaining the object above, the present invention is avehicle motion control system capable of independently controllingdriving forces and braking forces of four wheels, comprising: a firstmode in which substantially the same driving force and braking force aregenerated with respect to left and right wheels among the four wheelsbased on a longitudinal acceleration/deceleration control command thatis coordinated with a lateral motion of the vehicle; and a second modein which different driving forces and braking forces are generated withrespect to the left and right wheels among the four wheels based on atarget yaw moment derived from sideslip information of the vehicle,wherein the first mode is selected when the target yaw moment is equalto or less than a predefined threshold, and the second mode is selectedwhen the target yaw moment is greater than the threshold.

Effects of the Invention

A vehicle drive control system that feels less unnatural and enables animprovement in safety performance may be provided.

The present specification incorporates the contents of the specificationand/or drawings of JP Patent Application No. 2009-225938 from which thepresent application claims priority.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the overall configuration of a vehiclemotion control system according to the present invention.

FIG. 2 is a diagram showing lateral acceleration and lateral jerkestimation using a vehicle model of the present invention.

FIG. 3 is a diagram showing lateral acceleration and lateral jerkestimation using an acceleration sensor of the present invention.

FIG. 4 is a diagram showing a concept of the present invention whereestimated signals and measured signals complement each other.

FIG. 5 is a diagram showing a process from entry to exit for a leftcorner with respect to a G-vectoring controlled vehicle of the presentinvention.

FIG. 6 shows charts indicating time series data from when the travelpath in FIG. 5 is traveled.

FIG. 7 is a diagram showing the application of a positive yawing momentby left and right differential braking forces/driving forces of thepresent invention.

FIG. 8 is a diagram showing the application of a negative yawing momentby left and right differential braking forces/driving forces of thepresent invention.

FIG. 9 is a diagram showing a process from entry to exit for a leftcorner with respect to a sideslip prevention controlled vehicle of thepresent invention.

FIG. 10 shows charts indicating time series data from when the travelpath in FIG. 9 is traveled.

FIG. 11 is a diagram showing a control block of a vehicle motion controlsystem according to the present invention.

FIG. 12 is a diagram showing forces, accelerations and a yawing motionexerted on a vehicle.

FIG. 13 is a diagram showing yaw moments resulting from load shifts byG-Vectoring control of the present invention.

FIG. 14 is a diagram showing a flowchart for G-Vectoring control andsideslip prevention control of the present invention.

FIG. 15 shows charts indicating time series data during fused control ofG-Vectoring and sideslip prevention of the present invention.

FIG. 16 shows charts indicating time series data during fused control ofG-Vectoring and sideslip prevention of the present invention.

FIG. 17 is a diagram showing control effects of the present inventionobserved in a “g-g” diagram.

FIG. 18 is a diagram showing a situation where a mountainous area in asnowy region is being traveled.

FIG. 19 is a diagram showing a situation where a slope is beingdescended.

FIG. 20 is a diagram showing a longitudinal acceleration feedback loopof the present invention.

FIG. 21 is a diagram showing a situation where a bumpy road is traveled.

FIG. 22 shows charts indicating changes in steer response due to changesin road surface characteristics.

FIG. 23 is a diagram showing a control selector and multi-informationdisplay of the present invention.

LIST OF REFERENCE NUMERALS

-   0 Vehicle-   1 Motor-   2 Driving force distribution mechanism-   7 Power steering-   10 Accelerator pedal-   11 Brake pedal-   16 Steering-   21 Lateral acceleration sensor-   22 Longitudinal acceleration sensor-   23, 24, 25 Differentiating circuit-   31 Accelerator sensor-   32 Brake sensor-   33 Steering angle sensor-   38 Yaw rate sensor-   40 Central controller-   44 Steering controller-   46 Power train controller-   48 Pedal controller-   51 Accelerator reaction motor-   52 Brake reaction motor-   53 Steering reaction motor-   61 Left front wheel-   62 Right front wheel-   63 Left rear wheel-   64 Right rear wheel-   70 Millimeter wave vehicle ground speed sensor-   81 Control selector-   82 Multi-information display-   121 Left front wheel motor-   122 Right front wheel motor-   451, 452 Brake controller

BEST MODES FOR CARRYING OUT THE INVENTION

The overall configuration of an embodiment of a vehicle motion controlsystem of the present invention is shown in FIG. 1.

In the present embodiment, a vehicle 0 is of a so-called by-wire system,and there is no mechanical link between the driver and the steeringmechanism, acceleration mechanism and deceleration mechanism.

<Driving>

The vehicle 0 is a four-wheel-drive vehicle (All Wheel Drive: AWDvehicle) that drives a left rear wheel 63 and a right rear wheel 64 witha motor 1, while driving a left front wheel 61 with a left front wheelmotor 121, and a right front wheel 62 with a right front wheel motor122. A driving force distribution mechanism 2 capable of freelydistributing the torque of the motor across the left and right wheels isso mounted as to be connected with the motor 1. Differences in powersource, e.g., electric motors, internal combustion engines, etc., arenot particularly relevant to the present invention. As a most suitableexample representing the present invention, and by being combined withthe later-discussed four-wheel independent brake, the configuration issuch that the driving forces and braking forces of the four wheels arefreely controllable. The configuration is presented in detail below.

The left front wheel 61, the right front wheel 62, the left rear wheel63, and the right rear wheel 64 are each equipped with a brake rotor, awheel speed sensing rotor, and, on the vehicle-side, a wheel speedpickup, thereby providing a configuration that allows the wheel speed ofeach wheel to be sensed. Then, the amount by which the driver steps onan accelerator pedal 10 is sensed by an accelerator position sensor 31,and is processed at a central controller 40, which is a vehicle motioncontrol system, via a pedal controller 48. This processing includestherein torque distribution information that is in accordance with“sideslip prevention control” as an object of the present invention.Then, in accordance with this amount, a power train controller 46controls the outputs of the motor 1, the left front wheel motor 121, andthe right front wheel motor 122. In addition, the output of the motor 1is distributed across the left rear wheel 63 and the right rear wheel 64at the optimal ratio via the driving force distribution mechanism 2,which is controlled by the power train controller 46.

An accelerator reaction motor 51 is also connected to the acceleratorpedal 10, and reactions are controlled by the pedal controller 48 basedon a computed command of the central controller 40.

It is noted that the central controller 40, which is a vehicle motioncontrol system, is a vehicle motion control system capable ofindependently controlling the driving forces and braking forces of thefour wheels.

<Braking>

The left front wheel 61, the right front wheel 62, the left rear wheel63, and the right rear wheel 64 are each equipped with a brake rotor,and, on the vehicle-side, a caliper that decelerates the wheel bypinching the brake rotor with pads (not shown). The caliper ishydraulic, or electric with an electric motor for each caliper.

Each caliper is controlled by a brake controller 451 (for the frontwheels) or 452 (for the rear wheels) based generally on a computedcommand of the central controller 40.

A brake reaction motor 52 is also connected to the brake pedal 11, andreactions are controlled by the pedal controller 48 based on a computedcommand of the central controller 40.

<Integrated Control of Braking and Driving>

With the present invention, braking forces and driving forces thatdiffer between the left and right wheels would be generated based onsideslip angle information, however, what contributes as a yaw moment isthe difference between the left and right braking forces or drivingforces. Accordingly, in order to create this difference, there may beunordinary operations, such as driving one side while braking the other.An integrated control command under such circumstances is such that acommand is determined in an integrated manner by the central controller40 and appropriately controlled via the brake controllers 451 (for thefront wheels) and 452 (for the rear wheels), the power train controller46, the motor 1, and the driving force distribution mechanism 2.

<Steering>

The steering system of the vehicle 0 is of a steer-by-wire structurewhere there is no mechanical link between the driver's steering angleand the tire turning angle. It comprises power steering 7, whichincludes therein a steering angle sensor (not shown), steering 16, adriver steering angle sensor 33, and a steering controller 44. Theamount by which the driver steers the steering 16 is sensed by thedriver steering angle sensor 33, and is processed at the centralcontroller 40 via the steering controller 44. In accordance with thisamount, the steering controller 44 then controls the power steering 7.

A steer reaction motor 53 is also connected to the steering 16, andreactions are controlled by the steering controller 44 based on acomputed command of the central controller 40.

The amount by which the driver steps on the brake pedal 11 is sensed bya brake pedal position sensor 32, and is processed at the centralcontroller 40 via the pedal controller 48.

<Sensors>

A group of motion sensors of the present invention are next discussed.With respect to sensors that measure the motion of the vehicle in thepresent embodiment, there are provided an absolute vehicle speed meter,a yaw rate sensor, an acceleration sensor, etc. In addition to the aboveand at the same time, vehicle speed and yaw rate are estimated with awheel speed sensor, yaw rate and lateral acceleration are estimatedusing vehicle speed, steering angle, and vehicle motion models, and soforth.

The vehicle 0 is equipped with a millimeter wave vehicle ground speedsensor 70, and longitudinal speed V_(x) and lateral speed V_(y) may besensed independently. In addition, the wheel speed of each wheel isinputted to the brake controller 451 or 452 as mentioned above. Based onthe wheel speeds of the four wheels, the absolute vehicle speed may beestimated by averaging the wheel speeds of the front wheels (non-drivenwheels). With respect to the present invention, the configuration issuch that the absolute vehicle speed (V_(x)) is measured accurately,even in cases where all four wheels decrease in wheel speed at the sametime, by using the method disclosed in JP Patent Application Publication(Kokai) No. 5-16789 A (1993) and adding signals of the wheel speeds andof an acceleration sensor that senses the vehicle's longitudinalacceleration. In addition, it also incorporates a feature that estimatesthe yaw rate of the vehicle body by obtaining the difference between theleft and right wheel speeds of the front wheels (non-driven wheels),thereby improving the robustness of sensing signals.

These signals are then constantly monitored within the centralcontroller 40 as shared information. The configuration is such that theestimated absolute vehicle speed is compared and referenced against thesignal of the millimeter wave vehicle ground speed sensor 70, and eachcomplements the other if some anomaly were to occur in either of thesignals.

As shown in FIG. 1, the lateral acceleration sensor 21, the longitudinalacceleration sensor 22, and the yaw rate sensor 38 are disposed near thecenter of gravity. In addition, there are provided differentiatingcircuits 23 and 24 which obtain jerk information by differentiating theoutputs of their respective acceleration sensors. There is furtherprovided a differentiating circuit 25 for obtaining a yaw angularacceleration signal by differentiating the sensor output of the yaw ratesensor 38.

In the present embodiment, in order to make the presence of thedifferentiating circuits clear, each sensor is shown to be provided withone. However, in reality, acceleration signals may be inputted directlyto the central controller 40, and differentiation processes may beperformed after various processes have been performed. Thus, using theyaw rate estimated based on the above-mentioned wheel speed sensors, theyaw angular acceleration of the vehicle body may be obtained byperforming a differentiation process within the central controller 40.

In addition, although acceleration sensors and differentiating circuitsare used in order to obtain jerk, the jerk sensor disclosed in JP PatentApplication No. 2002-39435 may be used instead.

In addition, the present embodiment also employs a method of estimatinglateral acceleration and lateral jerk. A method of estimating lateralacceleration estimated value G_(ye) and lateral jerk estimated valueG_(ye) _(—) dot based on steering angle δ is discussed using FIG. 2.

First, with respect to a vehicle lateral motion model, with steeringangle δ [deg] and vehicle speed V [m/s] as input, yaw rate r during asteady circular turn disregarding dynamic characteristics is calculatedas follows (Eq. 2).

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 2} \right\rbrack & \; \\{r = {\frac{1}{1 + {AV}^{2}}\frac{V}{I}\delta}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

With respect to the equation above, stability factor A and wheel base 1are parameters unique to the vehicle, and are empirically derivedconstant values. In addition, lateral acceleration G_(y) of the vehiclemay be represented through the following equation, (Eq. 3), where V isthe vehicle speed, β_dot the rate of change in the vehicle's sideslipangle, and r the yaw rate.

[Eq. 3]

G _(y) =V({dot over (β)}+r)≈V·r({dot over (β)}=β_dot)  (Eq. 3)

β_dot is a motion within the linear range of tire force, and is aquantity that may be omitted as being negligible. Here, lateralacceleration G_(ye-wod) is calculated by multiplying yaw rate r, forwhich dynamic characteristics have been disregarded as mentionedearlier, by vehicle speed V. This lateral acceleration does not takeinto account the dynamic characteristics of the vehicle having responselag characteristics in the low frequency region. This is for thefollowing reason. In order to obtain lateral jerk information G_(y) _(—)dot of the vehicle, time-discrete differentiation needs to be performedon lateral acceleration G_(y).

In so doing, the noise component of the signal is reinforced. In orderto use this signal for control, it has to be passed through a low-passfilter (LPF), which would, however, cause a phase lag. As such, adecision was made to derive jerk by employing a method whereacceleration with an earlier phase than the actual acceleration, and forwhich dynamic characteristics are disregarded, is calculated, and passedthrough an LPF with time constant T_(lpfe) after undergoing discretedifferentiation. Another way of looking at the above is that the lagcaused by the LPF represents the dynamic characteristics of lateralacceleration, and the acceleration thus derived is simplydifferentiated. Lateral acceleration G_(y) is also passed through an LPFwith the same time constant T_(lpf). This would be equivalent to havingdynamic characteristics imparted to acceleration as well, and, althoughnot shown in the drawings, it has been confirmed that in the linearrage, actual acceleration response is favorably represented.

A method in which lateral acceleration and lateral jerk are thuscalculated using the steering angle is advantageous in that theinfluence of noise is suppressed, while reducing the response lag oflateral acceleration and lateral jerk.

However, since this estimation method omits sideslip information of thevehicle and ignores non-linear characteristics of tires, should thesideslip angle become significant, it would be necessary to measure andutilize the actual lateral acceleration of the vehicle.

FIG. 3 shows a method of obtaining lateral acceleration G_(ys) andlateral jerk information G_(ys) _(—) dot for control using sensed signalG_(yso) of the lateral acceleration sensor 21. Since it contains noisecomponents, e.g., bumps on the road surface, etc., the sensor signalalso needs to be passed through a low-pass filter (time constantT_(lpfs)) (not for dynamics compensation).

In order to balance the above-discussed respective merits of estimatingand of measuring lateral acceleration and jerk, in the presentembodiment, a method is employed where both signals are used in acomplementary fashion as shown in FIG. 4. An estimated signal (indicatedwith the index “e” for “estimated”) and a sensed signal (indicated withthe index “s” for “sensed”) are to be multiplied by a gain, which variesbased on sideslip information (sideslip angle β, yaw rate r, etc.), andadded.

This variable gain K_(je) (where K_(je)<1) with respect to lateral jerkestimated signal G_(ye) _(—) dot is so varied as to assume a greatervalue in a region where the sideslip angle is small, and to assume asmaller value as sideslip increases.

In addition, variable gain K_(js) (where K_(js)<1) with respect tolateral jerk sensed signal G_(ys) _(—) dot is so varied as to assume asmaller value in a region where the sideslip angle is small, and toassume a greater value as sideslip increases.

Similarly, variable gain K_(ge) (where K_(ge)<1) with respect to lateralacceleration estimated signal G_(ye) is so varied as to assume a greatervalue in a region where the sideslip angle is small, and to assume asmaller value as sideslip increases. In addition, variable gain K_(gs)(where K_(gs)<1) with respect to lateral acceleration sensed signalG_(ys) is so varied as to assume a smaller value in a region where thesideslip angle is small, and to assume a greater value as sideslipincreases.

By adopting such a configuration, there is provided a configuration inwhich noise is low in regions ranging from the normal region where thesideslip angle is small and up to the critical region where sideslip hasbecome significant, and in which acceleration and jerk signals suitablefor control may be obtained. It is noted that these gains are determinedthrough a sideslip information function or map.

A system configuration and a method of estimating lateral accelerationand lateral jerk according to the first embodiment of the presentinvention have thus far been discussed (and these are incorporated aslogic within the central controller 40). Hereinbelow, a “longitudinalacceleration/deceleration control command coordinated with lateralmotion” and a “yaw moment control command calculated derived fromsideslip information of the vehicle” are discussed.

<Longitudinal Acceleration/Deceleration Control Command Coordinated withLateral Motion: G-Vectoring>

An outline of acceleration/deceleration control coordinated with lateralmotion is, for example, presented in Non-Patent Document 1.

It is basically a simple control rule where lateral jerk G_(y) _(—) dotis multiplied by gain C_(xy), and a value to which a first-order lag isimparted is taken to be a longitudinal acceleration/deceleration controlcommand. It is confirmed in Non-Patent Document 2 that a lateral andlongitudinal motion coordinated control strategy of an expert driver maythus be partially simulated.

G_(x) _(DC) in (Eq. 1) is a deceleration component that is notcoordinated with lateral motion (an acceleration/deceleration commandthat is inputted by the driver or automatically based on externalinformation). It is a term that is required in cases where there isanticipatory deceleration when a corner is ahead or where there is azone speed command. It is noted that longitudinalacceleration/deceleration control command G_(xc) is equivalent to targetlongitudinal acceleration/deceleration control command G_(xt).

Further, the sgn (signum) term is a term provided so that the operationabove may be attained with respect to both right corners and leftcorners. Specifically, an operation may be attained where decelerationis performed at turn-in upon starting steering, deceleration issuspended once at steady turn (since lateral jerk becomes zero), andacceleration is performed upon starting to ease steering when exitingthe corner. Accelerating/decelerating in accordance with lateral jerkmay be construed as decelerating when lateral acceleration increases andaccelerating when lateral acceleration decreases.

Further, drawing on (Eq. 2) and (Eq. 3), it may also be construed tomean that the vehicle decelerates when the steering angle increases, andthat the vehicle accelerates when the steering angle decreases.

When thus controlled, with respect to a diagram whose horizontal axisrepresents the longitudinal acceleration of the vehicle and the verticalaxis the lateral acceleration of the vehicle, the combined acceleration(denoted by G) of longitudinal acceleration and lateral acceleration isso oriented (vectored) as to transition in a curved manner with thepassage of time. It is therefore called “G-Vectoring control.”

Vehicle motion with respect to a case where the control of (Eq. 1) isapplied is described assuming a specific case of traveling. FIG. 5assumes a common travel scene where a corner is entered and exited,namely, straight road A, transition zone B, steady turn zone C,transition zone D, and straight zone E. In this case, it is assumed thatno acceleration/deceleration operation is performed by the driver.

In addition, FIG. 6 shows charts where steering angle, lateralacceleration, lateral jerk, longitudinal acceleration/decelerationcontrol command as calculated through (Eq. 1), and the brakingforces/driving forces of the four wheels (61, 62, 63, 64) arerepresented as time history waveforms. With respect to the front outerwheel (62 in the case of a left turn) and the front inner wheel (61), aswell as the rear outer wheel (64) and rear inner wheel (63), brakingforces and driving forces are so distributed as to assume the same valuebetween the left and the right (the inner side and the outer side). Thiswill be discussed in detail later.

The term braking force/driving force is used herein to collectivelyrefer to forces of the respective wheels that are generated in thevehicle longitudinal direction, where braking force is defined as aforce in a direction that decelerates the vehicle, and driving force asa force in a direction that accelerates the vehicle.

First, the vehicle enters the corner from straight road zone A. Intransition zone B (point 1 to point 3), as the driver graduallyincreases steering, the vehicle's lateral acceleration G_(y) increases.Lateral jerk G_(y)dot assumes a positive value while lateralacceleration is increasing near point 2 (and returns to zero at 3, atwhich point lateral acceleration ceases to increase).

In this case, according to (Eq. 1), as lateral acceleration G_(y)increases, a deceleration (G_(xc) is negative) command is generated withrespect to the controlled vehicle. In accordance therewith, brakingforces (with a minus sign) of generally the same magnitude would beapplied to the front outer, front inner, rear outer, and rear innerwheels.

Then, as the vehicle enters steady turn zone C (point 3 to point 5), thedriver stops increasing steering, thereby maintaining a constantsteering angle. In so doing, since lateral jerk G_(y) _(—) dot becomes0, longitudinal acceleration/deceleration control command G_(xc) becomes0. Accordingly, the braking forces/driving forces on the wheels alsobecome zero.

Next, in transition zone D (points 5 to 7), due to the driver's easingof steering, the vehicle's lateral acceleration G_(y) decreases. At thispoint, the vehicle's lateral jerk G_(y) _(—) dot is negative, and,according to (Eq. 1), longitudinal acceleration/deceleration controlcommand G_(xc) is generated with respect to the controlled vehicle. Inaccordance therewith, driving forces (with a plus sign) of generally thesame magnitude would be applied to the front outer, front inner, rearouter, and rear inner wheels.

Further, in straight zone E, lateral jerk G_(y) becomes 0, and lateraljerk G_(y) _(—) dot also becomes zero. Consequently, noacceleration/deceleration control is performed. Thus, deceleration takesplace from turn-in (point 1) upon starting steering up to the clippingpoint (point 3), deceleration is suspended during the steady circularturn (point 3 to point 5), and acceleration takes place from when theeasing of steering starts (point 5) up to when the corner is exited(point 7). Thus, by applying G-Vectoring control to the vehicle, thedriver would be able to attain an acceleration/deceleration motion thatis coordinated with lateral motion by simply performing steering to makea turn.

In addition, when this motion is represented in a “g-g” diagramdepicting the acceleration mode occurring with respect to the vehicle,where the horizontal axis represents longitudinal acceleration and thevertical axis lateral acceleration, a characteristic motion thattransitions in a smooth and curved fashion is observed. This signifiesthat the longitudinal acceleration/deceleration control command is sodetermined as to transition in a curved fashion in the diagram with thepassage of time. With respect to left corners, this curved transitionwould be a clockwise transition as shown in the diagram. With respect toright corners, the transition path is inverted about the G_(x) axis, andits transition direction becomes anti-clockwise. When a transitionoccurs in this manner, the pitching motion that is generated withrespect to the vehicle due to longitudinal acceleration is favorablycoordinated with the rolling motion that is generated due to lateralacceleration, and peak values for the roll rate and pitch rate arereduced.

<Yaw Moment Control Command>

Next, yaw moment control based on left/right wheel driving force/brakingforce distribution is briefly presented using the drawings. FIG. 7 showsschematic diagrams depicting a situation where a yaw moment in an inturning direction (positive) is inputted with respect to ananti-clockwise turn steady state (A) of the vehicle 0. First, a lateralmotion equation and yawing (rotating) motion equation for the vehicle 0in the steady state are provided below as (Eq. 4) and (Eq. 5).

[Eq. 4]

mG _(y) =F _(yf) +F _(yr)  (Eq. 4).

[Eq. 5]

M=I _(z) {dot over (r)}=0=F _(yf) l _(f) −F _(yr) l _(r)({dot over(r)}_dot)  (Eq. 5).

where m is the mass of the vehicle 0, G_(y) the lateral accelerationexerted on the vehicle 0, F_(yf) the lateral force of the two frontwheels, F_(yr) the lateral force of the two rear wheels, M the yawmoment, I_(Z) the yawing moment of inertia of the vehicle 0, r_dot theyaw angular acceleration of the vehicle 0 (r being the yaw rate), l_(f)the distance between the center of gravity of the vehicle 0 and thefront axle, and l_(r) the distance between the center of gravity of thevehicle 0 and the rear axle. During a steady circular turn, the yawingmotion balances out (the yaw moment is zero), and angular accelerationbecomes zero.

From this state, (B) is an example where a brake is applied only to theinner rear wheel (the left rear wheel 63) thereby imparting brakingforce (F_(xrl)), (C) is an example where, in addition to the above, abrake is also applied to the inner front wheel thereby imparting brakingforce (F_(xfl)), and (D) is an example where, in addition to (C),driving forces (F_(fxr), F_(xrr)) are imparted to the outer front andrear wheels. In this case, the yawing moment of (Eq. 6) below would acton the vehicle 0.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 6} \right\rbrack & \; \\\begin{matrix}{M_{d} = {\frac{d}{2}\left\{ {\left( {F_{xfr} + F_{xrr}} \right) - \left( {F_{xfl} + F_{xrl}} \right)} \right\}}} \\{= {{\frac{d}{2}\left( {F_{xr} - F_{xl}} \right)} > 0}}\end{matrix} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

In the equation above, forces in the forward direction, i.e., thedriving direction, are defined as being positive, and forces in thebraking direction negative, where d represents the distance (tread)between the left and right wheels. Further, the combined brakingforce/driving force of the left front and rear wheels is denoted byF_(xl), and the combined braking force/driving force of the right frontand rear wheels by F_(xr).

Similarly, FIG. 8 shows a distribution of braking forces/driving forcesthat generates a negative direction, i.e., clockwise (restoring side),yaw moment when there is a negative moment, that is, when a left turn isbeing made. In this case, too, the equation for the yawing motion wouldbe (Eq. 6).

With respect to the vehicle 0, since it is possible to freely generatebraking and driving forces for each of the four wheels via commands bythe central controller 40, both positive and negative yaw moments may begenerated.

With the present invention, it is assumed that, when the vehicle'smeasured longitudinal acceleration G_(x) and lateral acceleration G_(y)are indicated in a diagram where the positive direction and negativedirection of the horizontal axis respectively represent the vehicle'sacceleration and deceleration, and where the positive direction andnegative direction of the vertical axis respectively represent thevehicle's leftward lateral acceleration and rightward acceleration, iftarget yaw moment M_(t) is a clockwise value as viewed from above thevehicle, either a greater decelerating force is imparted to the leftwheels relative to the right wheels or a greater driving force isimparted to the right wheels relative to the left wheels, whereas iftarget yaw moment M_(t) is an anti-clockwise value as viewed from abovethe vehicle, either a greater decelerating force is imparted to theright wheels relative to the left wheels or a greater driving force isimparted to the left wheels relative to the right wheels.

In addition, it is assumed that, when the vehicle's measuredlongitudinal acceleration G_(x) and lateral acceleration G_(y) areindicated in a diagram where the positive direction and negativedirection of the horizontal axis respectively represent the vehicle'sacceleration and deceleration, and where the positive direction andnegative direction of the vertical axis respectively represent thevehicle's leftward lateral acceleration and rightward acceleration, thelongitudinal acceleration/deceleration is determined in accordance withthe lateral motion in such a manner that a clockwise curved transitionwould be observed with the passage of time when starting ananti-clockwise motion as viewed from above the vehicle, whereas ananti-clockwise curved transition would be observed with the passage oftime when starting a clockwise motion as viewed from above the vehicle.

Next, with respect to a specific case of traveling, the application ofsuch yaw moment control to “sideslip prevention” is described includingan overview of the operating conditions thereof. With respect to atravel scene where a corner is entered and exited, namely, straight roadA, transition zone B, steady turn zone C, transition zone D, andstraight zone E, FIG. 9 shows the results of performing “sideslipprevention control” in a situation where, as provided below,“understeer” and “oversteer” occur to cause the vehicle to sideslip andfall off course.

Using the three yaw rates and the sideslip angle in FIG. 10, a briefdescription is provided with respect to the judgment of “understeer” and“oversteer.” FIG. 10 shows charts where the steering angle, the yawrates including estimated values and the estimated vehicle sideslipangle, which are to be used for “sideslip prevention control”intervention conditions, the yaw moment command derived from the above,the braking forces/driving forces of the four wheels (61, 62, 63, 64),and the vehicle longitudinal acceleration and lateral acceleration inthis case are represented as time history waveforms.

First, yaw rate r_(δ) derived from steering is calculated through (Eq.2) using stability factor A, wheel base 1, vehicle speed V, and steeringangle δ. Since it takes the driver's steering angle as input, it may besaid that it best reflects the driver's intention.

Next, yaw rate r_(Gy) derived from lateral acceleration is calculated byomitting, as in (Eq. 3), sideslip angle change β_dot to obtain (Eq. 7),and dividing lateral acceleration by vehicle speed.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 7} \right\rbrack & \; \\{r_{G_{y}} = \frac{G_{y}}{V}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

This value may be thought of as an indication of the vehicle's orbitalspeed, and may be thought of as a quantity indicating a vehicle turnlimit.

Further, yaw rate r_(s) sensed by the yaw rate sensor 38 indicates theactual rotating speed of the vehicle.

While sideslip angle β is by definition obtained by calculatingarctan(v/u) using the vehicle's longitudinal speed u and the vehicle'slateral speed v, it may be thought of as the angle formed between thevehicle and the travel direction. By way of example, the arrows passingthrough the vehicle's center of gravity in FIG. 7 and FIG. 8 indicatethe vehicle's travel direction, and the angle formed between that andthe vehicle's longitudinal direction is the sideslip angle, where theanti-clockwise direction with respect to the vehicle fixed coordinatesystem is taken to be positive. FIG. 7 shows a state where the sideslipangle is negative and significant, and where oversteer→spin is induced.Conversely, FIG. 8 shows a state where the sideslip angle is positiveand significant, and where understeer→k path departure is induced.

Sideslip angle β_(δ) derived from steering may be calculated as in (Eq.8) below using a vehicle motion model.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 8} \right\rbrack & \; \\{\delta = {\frac{1 - {\frac{m}{2l}\frac{l_{f}}{l_{r}K}V^{2}}}{1 + {AV}^{2}}\frac{l_{r}}{l}\delta}} & \left( {{Eq}.\mspace{14mu} 8} \right)\end{matrix}$

where m is the vehicle mass, and Kr the cornering stiffness representingthe lateral force gain per unit sideslip angle of the rear wheels.

The sideslip angle may be calculated through (Eq. 9) below byindependently sensing longitudinal speed V_(x) and lateral speed V_(y)with the millimeter wave vehicle ground speed sensor 70, or anintegration method such as (Eq. 10) may be used.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 9} \right\rbrack & \; \\{\beta = {\arctan \left( \frac{V_{y}}{V_{x}} \right)}} & \left( {{Eq}.\mspace{14mu} 9} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 10} \right\rbrack & \; \\{{\int{\overset{.}{\beta}{t}}} = {\int{\left( {\frac{G_{y}}{V_{x}} - r} \right){t}}}} & \left( {{Eq}.\mspace{14mu} 10} \right)\end{matrix}$

Using yaw rate r_(δ) derived from steering, yaw rate r_(Gy) derived fromlateral acceleration, yaw rate r_(s) sensed with the yaw rate sensor 38,sideslip angle β_(δ) derived from steering, and sideslip angle β derivedfrom sensed or estimated values, (1) “sideslip prevention control”intervention conditions and (2) yaw moment control amount are determinedusing a method similar to that disclosed in JP Patent ApplicationPublication (Kokai) No. 09-315277 A (1997).

(1) Intervention Conditions

The yaw rate derived from lateral acceleration is compared with theactual yaw rate, and it is determined to be understeer when the actualyaw rate is smaller, and oversteer when greater, and, further, oversteerwhen the sideslip angle is negative and large. The threshold, dead zone,etc., for the above are adjusted through sensory tests on test drivers,etc.

(2) Yaw Moment Control Amount

A yaw moment is generally applied in such a manner that the yaw rate andsideslip angle derived from steering would be close to the actualvalues. Further, the sideslip angle derivative value, etc., aremultiplied by a gain that has been so adjusted as to feel natural, andcorrections are made using their sum.

The occurrence of understeer and oversteer in the present embodiment,and “sideslip prevention control” with respect thereto will now bepresented using FIG. 10. First, at positions 2 and 3 in transition zoneB upon entering the corner, there is a possibility that understeer mayoccur and that the vehicle may deviate from the course. This may besensed from the fact that actual yaw rate r_(s) is less than yaw rater_(GY) derived from lateral acceleration. As such, a yaw moment commandin the in turning direction (positive) is calculated. Then, in thepresent embodiment, a braking force is generated with respect to theleft (inner) rear wheel, thereby applying a moment in the in turningdirection (positive). Due to this braking force, as indicated by thelongitudinal acceleration in FIG. 10 (second from the bottom),deceleration with a profile similar to that of the rear inner wheelbraking force would be at work.

In addition, in steady turn zone C, in a maximum lateral accelerationstate, the equivalent cornering stiffness of the rear wheels dropsrelatively, and oversteer occurs, thereby creating a situation likely totrigger spinning. This may be sensed from the fact that actual yaw rater_(s) is greater than yaw rate r_(Gy) derived from lateral acceleration,and it further may be sensed from the fact that the sideslip angle hasexceeded β_(th), which is the threshold. In order to restore the excessyawing motion, in the present embodiment, a braking force is generatedwith respect to both the right (outer) front wheel and rear wheel,thereby applying a clockwise moment. Due to this braking force, asindicated by the longitudinal acceleration in FIG. 10 (second from thebottom), deceleration with a profile similar to that of the sum of thebraking forces for the front outer wheel and the rear outer wheel wouldbe at work.

Braking forces are distributed among the front outer wheel (62 in thecase of a left turn), the front inner wheel (61), the rear outer wheel(64), and the rear inner wheel (63) so as to assume different valuesbetween the left and the right (inside and outside) only when thereexists a yaw moment command.

By thus controlling braking forces (driving forces) so as to assumedifferent values between the left and the right, it is possible toattain yaw moment control for preventing vehicle sideslip, therebyensuring vehicle maneuverability (tunability) and stability. However, asshown in FIG. 10, in this case, deceleration would occur depending onthe occurrence of sideslip. Naturally, since a change in speed, etc.,would also occur, fluctuation would occur in the lateral accelerationeven if the handle is steered smoothly as in FIG. 10.

When this motion is depicted in a “g-g” diagram indicating theacceleration mode occurring with respect to the vehicle, where thehorizontal axis represents longitudinal acceleration and the verticalaxis lateral acceleration, anti-clockwise loops would occur at twoplaces between 1 and 5 as shown in the lower part of FIG. 9. As such,the pitching motion and the rolling motion would be asynchronous,resulting in a jerky motion as compared to the motion under G-Vectoringcontrol in FIG. 5. It would be, so to speak, anacceleration/deceleration motion that is not coordinated with thelateral motion caused by driver input.

This is why a sense of speed loss and an unnatural feel would be caused.With respect to such problems, the present invention automaticallyperforms acceleration/deceleration in coordination with steeringoperations and which operates from the normal driving region(G-Vectoring), and seeks to fuse control in which sideslip is reliablyreduced in the critical driving region (sideslip prevention control),thereby causing less of an unnatural feel and enabling an improvement insafety performance. A specific control system configuration and methodare disclosed below.

<Fusion of G-Vectoring Control and “Sideslip Prevention Control”>

FIG. 11 schematically shows the relationship between a processingcontrol logic of the central controller 40 and an observer thatestimates the sideslip angle based on the vehicle 0, a group of sensorsand signals from the sensors (although processed within the centralcontroller 40). The logic as a whole generally comprises a vehiclelateral motion model 401, a G-Vectoring controller unit 402, a yawmoment controller unit 403, and a braking force/driving forcedistribution unit 404.

Using (Eq. 2), (Eq. 3) or (Eq. 8), the vehicle lateral motion model 401estimates the estimated lateral acceleration (G_(ye)), target yaw rater_(t), and target sideslip angle β_(t) based on steering angle δ that isinputted from the driver steering angle sensor 33 and on vehicle speedV. In the present embodiment, the settings are such that target yaw rater_(t) would be equal to yaw rate r_(δ) mentioned above which is derivedfrom steering.

With respect to the lateral acceleration and lateral jerk to be inputtedto the G-Vectoring controller 402, which is the first processing unit, alogic 410 that uses both signals in a complementary fashion as shown inFIG. 4 is adopted. The logic 410 is a logic that calculates lateralacceleration and lateral jerk based on the estimated lateralacceleration (G_(ye)) that has been estimated, and the actual lateralacceleration that has actually been measured.

Using the lateral acceleration and lateral jerk mentioned above and inaccordance with (Eq. 1), the G-Vectoring controller 402 determines, oftarget longitudinal acceleration/deceleration control command G_(Xt),the component that is coordinated with the present vehicle lateralmotion. Further, G_(x) _(—) _(DC), which is the deceleration componentthat is not coordinated with the present vehicle lateral motion, isadded to calculate target longitudinal acceleration/deceleration controlcommand G_(Xt), which is then outputted to the braking force/drivingforce distribution unit 404.

In this case, G_(x) _(—) _(DC) is a term that is required in cases wherethere is anticipatory deceleration when a corner is ahead or where thereis a zone speed command. The zone speed command is information that isdetermined by the coordinates at which the host vehicle lies. It maytherefore be determined by matching coordinate data obtained with a GPS,etc., against map information in which zone speed commands are listed.Next, as for anticipatory deceleration with respect to a corner ahead,although details of the sensing will be omitted in the presentembodiment, it may be attained by a method in which, by way of example,information on what lies ahead of the host vehicle, e.g., monocular orstereo cameras, laser or millimeter wave ranging radars, GPSinformation, etc., is taken in, and in which acceleration/decelerationis performed in accordance with future lateral motion (lateral jerk)that has not yet become apparent. Using a path with respect to forwardgaze distance and time, and deviation information with respect toanticipated host vehicle arrival position, a future steering angle isestimated in a manner similar to a so-called “driver model” thatdetermines steering angles. Then, by performing G-Vectoring as in(Eq. 1) in accordance with future lateral jerk that is likely to becaused with respect to the vehicle due to this steering operation(Preview G-Vectoring), it becomes possible to perform anticipatorydeceleration with respect to a corner ahead.

Next, with respect to the yaw moment controller 403, which is the secondprocessing unit, in accordance with a logic such as that mentionedearlier, target yaw moment M_(t) is calculated based on respectivedeviations Δr and Δβ between target yaw rate r_(t) (r_(δ)) and theactual yaw rate, and between target sideslip angle β_(t) and the actual(or estimated) sideslip angle, which is then outputted to the brakingforce/driving force distribution unit 404.

The braking force/driving force distribution unit 404 determines thebraking forces/driving forces (F_(xfl), F_(xfr), F_(xrl), F_(xrr)) forthe four wheels of the vehicle 0 based on target longitudinalacceleration/deceleration control command G_(xt) or on target yaw momentM_(t). In the following, a basic distribution rule will first bepresented. In addition to the above, the effects of indirect yaw momentcontrol (IYC), which is characteristic of the “G-Vectoring” control ofthe present invention will be described generally. Characteristic pointsto be careful of with respect to braking force/driving forcedistribution will be discussed.

First, using FIG. 12, motion equations for longitudinal motion, lateralmotion, and yawing motion are considered. In order to improve theclarity of the equations, with respect to braking force/driving forceand tire lateral force, the force for two wheels are redefined as in(Eq. 11), (Eq. 12), (Eq. 13), and (Eq. 14) below.

[Eq. 11]

F _(xr) =F _(xfr) +F _(xrr)  (Eq. 11)

[Eq. 12]

F _(xl) =F _(xfl) +F _(xrl)  (Eq. 12)

[Eq. 13]

F _(yf) =F _(yfl) +F _(yfr)  (Eq. 13)

[Eq. 14]

F _(yr) =F _(yrl) +F _(yrr)  (Eq. 14)

which result in (Eq. 15), (Eq. 16), and (Eq. 17) below.

<Longitudinal Motion>

[Eq. 15]

mG _(xt) =F _(xl) +F _(xr)  (Eq. 15)

<Lateral Motion>

[Eq. 16]

mG _(y) =F _(yf) +F _(yr)  (Eq. 16)

<Yawing Motion>

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 17} \right\rbrack & \; \\{{I_{z} \cdot \overset{.}{r}} = {\left( {{l_{f}F_{yf}} - {l_{r}F_{y\; r}}} \right) + {\frac{d}{2}\left( {F_{xr} - F_{xl}} \right)}}} & \left( {{Eq}.\mspace{14mu} 17} \right)\end{matrix}$

Further, a description regarding the target yaw moment and brakingforces/driving forces for the respective wheels would be as in (Eq. 18)below.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 18} \right\rbrack & \; \\{M_{t} = {\frac{d}{2}\left( {F_{xr} - F_{xl}} \right)}} & \left( {{Eq}.\mspace{14mu} 18} \right)\end{matrix}$

In this case, by linking the longitudinal motion (Eq. 15) and the yawingmoment (Eq. 18), they may be analytically solved as in (Eq. 19) and (Eq.20) below with two unknowns and two equations.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 19} \right\rbrack & \; \\{F_{xr} = {{\frac{m}{2}G_{xt}} + \frac{M_{t}}{d}}} & \left( {{Eq}.\mspace{14mu} 19} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 20} \right\rbrack & \; \\{F_{xl} = {{\frac{m}{2}G_{xt}} - \frac{M_{t}}{d}}} & \left( {{Eq}.\mspace{14mu} 20} \right)\end{matrix}$

Thus, it was possible to attain a distribution for the brakingforce/driving force of the two right front and rear wheels and for thebraking force/driving force of the two left front and rear wheels wherethe longitudinal acceleration/deceleration control command based on“G-Vectoring control” and the moment command based on “sideslipprevention control” are simultaneously attained. Next, these aredistributed across the front and rear wheels in accordance with thefront and rear wheel vertical load ratio. Assuming now that h is theheight of the sprung center of gravity of the vehicle 0 relative to theground, and that the vehicle 0 is accelerating/decelerating due totarget longitudinal acceleration/deceleration control command G_(xt),then the loads (W_(f), W_(r)) for the respective two wheels at the frontand the rear would respectively be given by (Eq. 21) and (Eq. 22) below.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 21} \right\rbrack & \; \\{W_{f} = \frac{{mgl}_{r} - {mhG}_{xt}}{l}} & \left( {{Eq}.\mspace{14mu} 21} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 22} \right\rbrack & \; \\{W_{r} = \frac{{mgl}_{f} + {mhG}_{xt}}{l}} & \left( {{Eq}.\mspace{14mu} 22} \right)\end{matrix}$

Thus, the braking forces/driving forces for the four wheels distributedin accordance with the load ratio would be given by (Eq. 23), (Eq. 24),(Eq. 25), and (Eq. 26) below.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 23} \right\rbrack & \; \\{F_{xfr} = {\frac{{gl}_{r} - {hG}_{xt}}{gl}\left( {{\frac{m}{2}G_{xt}} + \frac{M_{t}}{d}} \right)}} & \left( {{Eq}.\mspace{14mu} 23} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 24} \right\rbrack & \; \\{F_{xfl} = {\frac{{gl}_{r} - {hG}_{xt}}{gl}\left( {{\frac{m}{2}G_{xt}} - \frac{M_{t}}{d}} \right)}} & \left( {{Eq}.\mspace{14mu} 24} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 25} \right\rbrack & \; \\{F_{xrr} = {\frac{{gl}_{f} + {hG}_{xt}}{gl}\left( {{\frac{m}{2}G_{xt}} + \frac{M_{t}}{d}} \right)}} & \left( {{Eq}.\mspace{14mu} 25} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 26} \right\rbrack & \; \\{F_{xrl} = {\frac{{gl}_{f} + {hG}_{xt}}{gl}\left( {{\frac{m}{2}G_{xt}} - \frac{M_{t}}{d}} \right)}} & \left( {{Eq}.\mspace{14mu} 26} \right)\end{matrix}$

However, (Eq. 27) and (Eq. 28) below hold true

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 27} \right\rbrack & \; \\{G_{xt} = {{{- {{sgn}\left( {G_{y} \cdot {\overset{.}{G}}_{y}} \right)}}\frac{C_{xy}}{1 + {Ts}}{{\overset{.}{G}}_{y}}} + G_{x\_ DC}}} & \left( {{Eq}.\mspace{14mu} 27} \right) \\\left\lbrack {{Eq}.\mspace{14mu} 28} \right\rbrack & \; \\{M_{t} = {M\left( {r_{\delta},r_{G_{y}},r_{s},\beta_{t},\beta_{s}} \right)}} & \left( {{Eq}.\mspace{14mu} 28} \right)\end{matrix}$

The details of (Eq. 28) are calculated using a method similar to thatdisclosed in JP Patent Application Publication (Kokai) No. 09-315277 A(1997).

The above is a basic distribution rule of the present invention. Lookingat (Eq. 23) through (Eq. 26), it may be construed that when the“G-Vectoring” control command value (target longitudinalacceleration/deceleration control command G_(xt)) is zero, the yawmoment command based on “sideslip prevention control” is distributed inaccordance with the static loads on the front and rear wheels, whereaswhen “G-Vectoring” control command value G_(xt) is not zero, the brakingforces and driving forces for attaining that longitudinal accelerationare distributed across the front and the rear at the load distributionratio with the left and right wheels being identical in value so as notto generate any excess moment.

With the central controller 40, which is a vehicle motion control systemof the present invention, fusion and decoupling of “G-Vectoringcontrol,” which works from the normal region, and a “sideslip preventionsystem,” which works in the critical region, become necessary.

When vehicle motion is considered as motion in a plane, it may bedescribed in terms of (1) longitudinal motion, (2) lateral motion, androtation about the center of gravity, that is, (3) yawing motion.“G-Vectoring control,” which attains acceleration/deceleration that iscoordinated with lateral motion, controls (1) longitudinalacceleration/deceleration, and does not directly control (3) the yawingmoment. In other words, the yawing moment is “arbitrary” and has somedegree of freedom.

In addition, the “sideslip prevention system” directly controls the (3)yaw moment, and does not control (1) acceleration/deceleration. In otherwords, longitudinal acceleration/deceleration is “arbitrary” and hassome degree of freedom.

Accordingly, in order to attain fusion of these controls, one maycontrol (1) longitudinal acceleration in accordance with anacceleration/deceleration control command coordinated with lateralmotion that is determined by “G-Vectoring control” and control (3)yawing moment in accordance with a yaw moment command determined by the“sideslip prevention control system.”

Specifically, a system is configured so as to have the following twomodes.

(1) In the normal region where sideslip is not pronounced, brakingforces/driving forces that are generally the same are generated withrespect to the left and right wheels based on a “G-Vectoring control”command (first mode).

(2) As sideslip increases, braking forces/driving forces that differbetween the left and the right are generated based on a yaw momentcommand determined through “sideslip prevention control” (second mode).

Then, when a state of the second mode is entered, if, for example, thelongitudinal acceleration caused by the braking forces/driving forces ofthe four wheels differs from the longitudinal acceleration commanddetermined through “G-Vectoring control,” the braking forces/drivingforces to be applied to the vehicle in order to generate that differenceacceleration are calculated, and values obtained by evenly distributingthem may be added to the left and right wheels. Thus, it is possible toattain the commanded acceleration/deceleration while maintaining thecommanded yawing moment (attaining fusion and decoupling of the twocontrols).

In other words, the present invention is able to provide a vehicle drivecontrol system comprising: a first mode (G-Vectoring control), in which,based on longitudinal acceleration/deceleration control command G_(xc)that is coordinated with the lateral motion of the vehicle, drivingforces and braking forces that are generally the same are generated withrespect to the left and right wheels among the four wheels thereof; anda second mode (sideslip prevention control), in which different drivingforces and braking forces are generated with respect to the left andright wheels among the four wheels based on target yaw moment M_(t)derived from the vehicle's sideslip information (steering angle δ,vehicle speed V, yaw rate r, and sideslip angle β), wherein the vehicledrive control system causes less of an unnatural feel and enables animprovement in safety performance by being of a configuration where thefirst mode is selected when target yaw moment M_(t) is equal to or lessthan pre-defined threshold M_(th), and where the second mode is selectedwhen the target yaw moment is greater than the threshold.

In addition, for example, in the case of two-wheel drive, or if the yawmoment is to be controlled through brake control only, there may becases where the desired driving force cannot be generated. In suchcases, the configuration is made to be such that safety is ensured byprioritizing “sideslip prevention control,” and reliably generating amoment.

Regarding the fusion of “G-Vectoring control” and “sideslip preventioncontrol” with respect to the present invention, there is one more pointthat should be considered, and that is the indirect yaw moment control(IYC) effect that stems from the load dependence of tire lateral force.This effect will be described generally using FIG. 13. It is assumed,for purposes of brevity, that l_(f) (the distance from the center ofgravity to the front axle) and l_(r) (the distance from the center ofgravity to the rear axle) are equal. In other words, it is assumed thatthe front and rear wheel loads of the front wheels and rear wheels atrest are equal.

As shown in FIG. 13, tire lateral force is proportional to tire sideslipangle when the sideslip angle is small, and has saturation propertieswhen the sideslip angle is large. Since it is assumed that the loads onthe front and rear wheels are equal, the same lateral force would begenerated for the same sideslip angle. Assuming now that the vehicle 0decelerates based on “G-Vectoring” control value G_(xt), the front wheelload increases as indicated in (Eq. 21), and the rear wheel loaddecreases as indicated in (Eq. 22). As a result, if deceleration occurswhile turning, lateral force F_(yf) of the front wheels increases, whilelateral force F_(yr) of the rear wheels decreases. Considering thisphenomenon based on the yawing motion equation of (Eq. 17), an inturning moment would be at work. In addition, if acceleration occurswhile turning, a yaw moment on the restoring side would be at work asshown in the lower part of FIG. 13.

With respect to “G-Vectoring” control that is coordinated with lateralmotion, as lateral acceleration increases, that is, as turning isstarted, deceleration occurs, thereby causing a yaw moment in thedirection for in turning. In addition, as lateral accelerationdecreases, that is, as turning is finished, acceleration occurs, therebycausing a yaw moment in the direction for restoring turning and headingstraight ahead. The above indicate that they both have potential forimproving maneuverability and stability.

If a yaw moment for “sideslip prevention control” were to be applied tosuch “G-Vectoring control,” there is a possibility that failure may becaused due to excess control amounts. By way of example, this may occurwhen a yaw moment for understeer prevention control is inputted from theperspective of “sideslip prevention control” upon entering a corner, and“G-Vectoring” control is further applied thereto, and so forth. Anotherconcern is that the control amount for understeer prevention may becometoo large, thereby going beyond neutral steer to become oversteer. Amethod of avoiding such situations will be described generally using theflowchart in FIG. 14.

First, vehicle speed V, yaw rate r, lateral acceleration G_(y), lateraljerk G_(y) _(—) dot, sideslip angle β, and sideslip angular speed β_dotare sensed or estimated (step (1)), and target longitudinalacceleration/deceleration control command G_(xt) that is based onG-Vectoring control rules and that is coordinated with lateral motion iscalculated (step (2)). Further, (1) intervention conditions and (2) acontrol amount, that is, target yaw moment M_(t), are calculated in sucha manner as to reduce the vehicle's sideslip (step (3)). A shortdescription will now be added with respect to target yaw moment M_(t).When sideslip occurs with respect to the vehicle, sideslip also occurswith respect to the front wheels and the rear wheels. As is well-known,under such circumstances, there is generated a cornering force that issubstantially proportional to cornering stiffness (unit: N/rad), whichrepresents a tire's lateral stiffness. A combined moment of a yaw momenton the in turning side, which may be expressed as the product of thecornering force generated by the front wheels and the distance from thevehicle's center of gravity to the front axle, and of a yaw moment onthe turn stopping side, which may be expressed as the product of thecornering force generated by the rear wheels and the distance from thevehicle's center of gravity to the rear axle, is a restoring yaw momentthat naturally occurs with respect to the vehicle when sideslip occurs.Accordingly, if the target yaw moment command is equal to or less thanthe restoring yaw moment, it would naturally converge to a state withlittle sideslip without having to apply any yaw moment control. Ifcontrol were to be applied under such conditions, it would create asubjective impression of overcontrol for the driver. In order to avoidsuch a phenomenon, a method is adopted where yaw moment control is notperformed at or below a threshold, which is the restoring yaw momentunique to the vehicle. With existing sideslip prevention systems, testdrives are repeatedly performed by test drivers, and this dead zone isset based on feeling evaluations. In other words, target yaw momentcommand M_(t) calculated in step (3) represents a specific controlcommand value for a situation where control is required and as a valuein or above the dead zone (if a value simply obtained from sideslipinformation is in or below the dead zone, M_(t) is made to be zero).This yaw moment command is a basic yaw moment command for a case whereno acceleration/deceleration is taking place.

Next, in step (4), a determination is made as to whether or not there isa longitudinal acceleration/deceleration control command. First, a casewhere there is a longitudinal acceleration/deceleration control command,that is, a case where a transition to step (5) is made, will bediscussed. In step (5), control rules are changed based on the magnitudeof target yaw moment M_(t). First, a comparison between target yawmoment M_(t) and M_(th), which is a pre-defined threshold, is made, andit is determined whether to perform yaw moment control where the brakingand driving forces of the left and right wheels are distributedindividually ((7) through (10)), or to perform only G-Vectoring (5)where generally equal braking and driving forces are distributed betweenthe left and right wheels.

As discussed above, although the restoring yaw moment for determiningthe dead zone may be set roughly based on tire characteristics andvehicle specifications, tire characteristics are dependent on load aswas discussed in connection with FIG. 13. Accordingly, taking intoconsideration the acceleration/deceleration state by G-Vectoringcontrol, which has potential for improving maneuverability andstability, the restoring yaw moment varies in an equivalent manner frommoment to moment, and the required yaw moment control amount becomeseven less. As such, in the present embodiment, threshold M_(th) isdefined with G-Vectoring control effects taken into consideration [seeNon-Patent Document 1] based on the load dependence coefficient of thetires. A comparison is then made with the absolute value of basic yawmoment command M_(t) determined in step (3), and the configuration issuch that if M_(t) is equal to or less than M_(th),acceleration/deceleration control is performed at an even distributionbetween the left and right wheels by G-Vectoring control (step (6)).

Thus, in the present embodiment, as shown in FIG. 14, the configurationis such that it includes a logic where, when G-Vectoring control isactive, the left/right distribution of braking forces and driving forcesis not performed unless the yaw moment control amount exceeds a giventhreshold. Consequently, when the yaw moment command is small, itoperates in the first mode (G-Vectoring (step (6)), and when the yawmoment command is large, it operates in the second mode (side slipprevention control (steps (7) through (10)).

In addition, the vehicle longitudinal acceleration attained in thesecond mode (sideslip prevention control) in which different brakingforces and/or driving forces are generated with respect to the left andright wheels among the four wheels is correctively controlled in such amanner that braking forces and/or driving forces that are substantiallyequal are applied to the left and right wheels among the four wheels sothat the difference with respect to the longitudinalacceleration/deceleration control command of (G-Vectoring) becomesnarrower (see also step (9) and (Eq. 23) through (Eq. 26)).

However, when other embodiments where brake/drive distribution is not atone's disposal, e.g., only brake control is performed with respect to anordinary two-wheel-drive vehicle (N in step (8)), etc., are considered,the vehicle longitudinal acceleration attained in the second mode(sideslip prevention control) in which different braking forces and/ordriving forces are generated with respect to the left and right wheelsamong the four wheels does not necessarily coincide with thelongitudinal acceleration/deceleration control command of (G-Vectoring).

By way of example, if brake control were to be performed when theG-Vectoring command is zero, deceleration would inevitably occur (step(10)). However, when the G-Vectoring control command is greater than thedeceleration caused by the sideslip prevention control command,corrective control may be performed in such a manner as to applysubstantially equal braking forces and/or driving forces to the left andright wheels among the four wheels so that the difference with respectto the G-Vectoring control command would be narrower. As such, thereexists a scene where a problem of the present invention is solved, andit therefore falls within the scope of the present invention.

In sum, the present invention is such that it is determined whether ornot target longitudinal acceleration/deceleration control command G_(xt)is zero. If target longitudinal acceleration/deceleration controlcommand G_(xt) is not zero and target yaw moment M_(t) is equal to orless than pre-defined threshold M_(th), the braking forces/drivingforces (F_(xfl), F_(xfr), F_(xrl), F_(xrr)) of the respective wheels ofthe vehicle are calculated at the braking force/driving forcedistribution unit 404 based on target longitudinalacceleration/deceleration control command G_(xt) in such a manner thatthe braking forces/driving forces of the left and right wheels would bedistributed in a substantially even manner. In addition, theconfiguration is such that, it is determined whether or not targetlongitudinal acceleration/deceleration control command G, is zero, andif target longitudinal acceleration/deceleration control command G_(xt)is zero, or if target longitudinal acceleration/deceleration controlcommand G_(xt) is not zero and target yaw moment M_(t) is greater thanpre-defined threshold M_(th), the braking forces/driving forces(F_(xfl), F_(xfr), F_(xrl), F_(xrr)) of the respective wheels of thevehicle are calculated at the braking force/driving force distributionunit 404 based on target yaw moment M_(t) in such a manner that thebraking forces/driving forces of the left and right wheels would bedistributed individually.

Finally, effects of the present invention will be described using FIG.15, FIG. 16, and FIG. 17. FIG. 15, FIG. 16, and FIG. 17 are examples inwhich the present invention is applied to the scene shown in FIG. 9 andFIG. 10 where only “sideslip prevention control” is applied. Inaddition, although the locations at which “understeer” and “oversteer”occur in FIG. 16 are the same as those in FIG. 10 and FIG. 15, there isassumed a case in which there is less fluctuation in the steercharacteristics.

FIG. 15 shows a longitudinal acceleration/deceleration control command,yaw moment control command, and brake/drive distribution of therespective wheels that are determined in accordance with the lateralmotion that occurs in accordance with the steering angle, and thevehicle yaw moment, vehicle longitudinal acceleration, and vehiclelateral acceleration that are brought about thereby. In this case, theyaw moment commands for reducing the understeer at locations 2 to 3 andthe oversteer at locations 4 to 5 are values with greater absolutevalues than control activating threshold M_(th) in step (5) in FIG. 14(“sideslip prevention control” is active). In the charts representingthe braking forces and driving forces of the respective wheels, thedotted line is the longitudinal acceleration/deceleration controlcommand of “G-Vectoring” control only, and the dashed line is thedeceleration amount based on the yaw moment command of “sideslipprevention control.” It can be seen that, through braking force/drivingforce distribution to which (Eq. 23) through (Eq. 26) of the presentinvention are applied, braking forces are applied to the four wheelsover the course of locations 1 to 3, causing an in turning moment. Itcan further be seen that, at location 2 and onward, a significantbraking force is applied only to the rear inner wheel, the brakingforces of the other wheels are reduced, and longitudinal accelerationfollows the “G-Vectoring” control command as netacceleration/deceleration, while the yaw moment demanded by “sideslipprevention control” is also attained. In addition, it can be seen that,at locations 4 to 5, the braking forces of the front outer wheel andrear outer wheel are reduced, driving forces are imparted to the frontinner wheel and rear inner wheel, and vehicle longitudinal accelerationfollows the “G-Vectoring” control command while yaw moment follows the“sideslip prevention control” command.

Likewise with respect to FIG. 16 for which a case is assumed where thereis less fluctuation in the steer characteristics, a yaw moment commandfor reducing understeer occurs across locations 2 to 3. However, sincethere is a longitudinal acceleration/deceleration control command whilethe yaw moment command is less than threshold M_(th), left/right wheelindependent braking control/driving control is omitted (the same brakingforce for the left and right wheels, step (6) in FIG. 14). In contrast,at locations 4 to 5, there is shown an example where “sideslipprevention control” is active because, although the yaw moment commandis less than threshold M_(th), there is no longitudinalacceleration/deceleration control command by “G-Vectoring,” and no loadshift occurs among the front and rear wheels (transition from step (4)to step (7) in FIG. 14). It can be seen that because the brakingforces/driving forces of the respective wheels are calculated using (Eq.23) through (Eq. 26) of the present invention, even in this state,vehicle longitudinal acceleration follows the “G-Vectoring” controlcommand, and yaw moment follows the “sideslip prevention control”command.

By having the braking forces and driving forces of the four wheelscontrolled as in FIG. 15 and FIG. 16, it is possible to attain acharacteristic motion that transitions in a smoothly curved fashion in a“g-g” diagram like “G-Vectoring” control while performing yaw momentcontrol for “sideslip prevention” as shown in FIG. 17. With respect toleft corners, this curved transition would be a clockwise transition asshown in the diagram, and for right corners, the transition path becomesinverted about the G_(x) axis, and its transition direction becomesanti-clockwise. When transitions occur in this manner, the pitchingmotion that occurs with respect to the vehicle due to longitudinalacceleration coordinates favorably with the rolling motion that occursdue to lateral acceleration, and the peak values for the roll rate andpitch rate are reduced. It can be seen that a technique and system thatcause less of an unnatural feel and enable an improvement in safetyperformance are successfully realized where acceleration/decelerationthat is coordinated with steering operations and that is advantageous inthe normal driving region is thus performed automatically, and wheresideslip is reliably reduced in the critical driving region.

It is of course necessary to consider situations in which the system orthe driver issues deceleration commands such as when a vehicle aheadstops abruptly, or when information is received that there is anobstacle on the road. In such situations, it is necessary that thesecommands be reflected with utmost priority. This may be done throughsystem input at the part where G_(x) _(DC) is added in the logic diagramin FIG. 11.

Up to this point, a situation in which the vehicle travels along a planewithout any bumps has been assumed, and a technique and system thatcause less of an unnatural feel and enable an improvement in safetyperformance have been disclosed where acceleration/deceleration that iscoordinated with steering operations and that is advantageous in thenormal driving region is performed automatically, and where sideslip isreliably reduced in the critical driving region. Specifically, a methodof controlling the braking forces/driving forces of the respectivewheels in such a manner that the vehicle motion follows both thelongitudinal acceleration command and the yaw moment command has beendisclosed assuming a situation in which the vehicle travels along aplane without any bumps.

Next, assuming a situation where a vehicle of the present invention istraveling a mountainous area in a snowy region as shown in FIG. 18, amore practical use situation of the present system is presented, and thecontent of what has been devised to solve practical control problems forobtaining control effects similar to those in a situation where thevehicle travels along a plane without any bumps will now be disclosed.

In situations like the one in FIG. 18, the following practical controlproblems arise.

(1) Change in vehicle longitudinal acceleration due to gravity componentbased on grade(2) Sense of jerkiness in acceleration/deceleration control stemmingfrom lateral acceleration caused by road surface bump input(3) Change in steer response due to change in road surfacecharacteristics

With respect to each of the above, problems will be clarified andsolutions with regard to the present invention will be disclosed.

(1) Change in Vehicle Longitudinal Acceleration Due to Gravity ComponentBased on Grade

Assuming that the vehicle weight is M, when a slope having an angle ofgrade θ is descended as shown in FIG. 19, a gravity component ofM_(g)·sin θ would be applied to the vehicle in the longitudinaldirection. If, with respect to longitudinal acceleration/decelerationcontrol command G_(xc), front wheel longitudinal force F_(xff) and rearwheel longitudinal force F_(xrr) were to be controlled by performingbrake fluid pressure control or motor torque control, etc., with anopen-loop, the actual vehicle deceleration, as opposed to thedeceleration command value, would become G_(x)=G_(xc)−M_(g)·sin θ,making it impossible to perform the intended control. In contrast to theabove, as shown in FIG. 20, actual longitudinal acceleration G_(x) maybe measured with the longitudinal acceleration sensor 22 and bemultiplied by gain K1, or be differentiated to find the longitudinaljerk, and the value obtained by multiplying it with gain K2 may becompared with target longitudinal acceleration/deceleration controlcommand G_(xt), and braking forces/driving forces F_(xff) and F_(xrr)may be determined based on deviation ΔG_(x) thereof. The “s” in K2s isthe Laplace operator, and feeds back a partial derivative to improveresponse.

(Gain K2 in this Case is Intended to Improve Control Readiness, and isnot an Essential Feature)

Further, if contemplating a system without the longitudinal accelerationsensor 22, the actual acceleration of the vehicle may be measured using,for example, derivatives of the wheel speed, and grade estimation may beperformed.

By configuring such a feedback loop, it is possible to have the actuallongitudinal acceleration follow the target longitudinal accelerationregardless of such disturbances as grade, etc., and control degradationmay be reduced.

Thus, even in a state where a road surface with a grade is beingtraveled, a motion that is in accordance with the targetacceleration/deceleration control command may be attained, and controleffects similar to those in situations where the vehicle is travelingalong a plane without any bumps may be obtained.

(2) Sense of Jerkiness in Acceleration/Deceleration Control Stemmingfrom Lateral Acceleration Caused by Road Surface Bump Input

In cases where, as shown in FIG. 21, the road surface is not flat andthe road shoulder portion is covered with frozen snow, should thevehicle run onto a bumpy road, the tires on the road shoulder side wouldconstantly be vibrated by the road surface, thereby generating smallkickback torques in the driver's steering angle, and steering anglechange Δδ would occur. In addition, small rolls would occur to causelateral acceleration change ΔG_(y) at the center of gravity, and noisewould consequently occur in the lateral jerk. If, under suchcircumstances, one were to adopt only a method such as that shown inFIG. 4, a small high-frequency component would be generated in thelongitudinal acceleration as shown in the diagram. In order to avoidsuch a situation, the present invention is so configured as to reducethe sense of jerkiness by using a threshold and not performing controlwith respect to longitudinal acceleration commands that are equal to orless than the threshold. In addition, although a threshold is definedwith respect to the absolute value of the longitudinal accelerationcontrol command in the present embodiment, as an idea in which athreshold is employed with respect to frequency, actual actuator controlmay also be performed based on vehicle longitudinal accelerationcommands that have been passed through a low-pass filter that onlyallows the frequency of the vehicle's lateral motion (2 Hz at most)through. It would thus be possible to reduce the sense of jerkiness inthe longitudinal direction even in cases where there are bumps in theroad.

(3) Change in Steer Response Due to Change in Road SurfaceCharacteristics

When the road surface traction condition changes at, for example, a snowsurface as shown in FIG. 22, discrepancies in amplitude and in phaseoccur respectively between the lateral acceleration and lateral jerk,which are estimated using a vehicle model with respect to steering anglesuch as that shown in FIG. 2, and the lateral acceleration actuallymeasured with the lateral acceleration sensor 21 and lateral jerkobtained as the time derivative thereof. In the low traction region, themeasured value is slightly delayed relative to the model estimatedvalue. In the previous embodiment, as shown in the drawings, a vehiclelongitudinal acceleration command that is coordinated with lateralmotion was formed using (Eq. 1) based on a linearly combined valueobtained by multiplying the lateral jerk that is based on a modelestimated value and the lateral jerk that is based on a measured valueby a gain and summing them up. If a compacted snow road were to betraveled by a vehicle thus configured, the feel on the hand at themoment when steering is begun and the turnability would be compromised.Further, deceleration would drop while the actual lateral accelerationis still increasing, and the continuity between the rolling motion andthe pitching motion would become diluted. Under such circumstances, thefeel on the hand as well as a sense of continuity of motion may besimultaneously attained by choosing the longitudinal acceleration using(Eq. 1) based on a signal obtained by so-called select-high, where theone with the greater amplitude is selected from the lateral jerk basedon a model estimated value, which has little response delay with respectto steering operations, and the measured lateral jerk, which iscoordinated with the vehicle's actual lateral motion. In addition, thesense of continuity of motion may be further improved by smoothing thecontrol command obtained by select-high by passing it through a low-passfilter.

Thus, there are provided a plurality of modes with distinct calculationmethods for target longitudinal acceleration/deceleration controlcommand G_(xt) depending on the traveled road surface, and there isprovided a switching means for switching between these plurality ofmodes.

As shown in FIG. 23, such switching of control modes may be done by thedriver with a control selector 81 (switching means) installed within thevehicle cabin. AUTOMATIC carries out mode switching automatically, andis configured in such a manner that linear combination, select-high, andthe respective gains for the lateral jerk based on a model estimatedvalue and for the lateral jerk based on a measured value are adjusted inaccordance with changes in road surface conditions, e.g., tractioncoefficient, etc. The configuration is such that, by way of example,braking force/driving force control is performed in accordance with alongitudinal acceleration command and the actual longitudinalacceleration is sensed, and if the actual longitudinal acceleration issignificantly less than the command value, it is determined as being acase where the traction coefficient is small, and select-high control isautomatically chosen, or the gain for the jerk on the model estimatedvalue side is increased, etc., thereby improving the feel on the hand.Such mode switching and gain switching may also be of mapped formats inaccordance with estimated traction coefficients. Thus, in accordancewith road surface conditions, it is possible to automatically obtaingood longitudinal acceleration/deceleration control commands coordinatedwith lateral motion. Further, although a detailed description is omittedin the present embodiment, this AUTOMATIC mode may be further dividedinto nimble mode in which the model estimated value jerk gain is setslightly high so that it would move nimbly in response to steering, andcomfort mode in which the jerk gain based on measured values is setslightly high to attain a laid-back motion, and so forth. In addition,external information may be incorporated to change the gain and mode asemergency avoidance mode.

Further, modes other than AUTOMATIC will be briefly described. Thesemodes are modes that the driver may choose from as desired.

TARMAC is intended mainly for use when traveling on dry paved roads, anda jerk linear combination mode is used. Since it has high responsivenessof vehicle motion with respect to steering, the model estimated lateraljerk and the lateral jerk based on measured values would be roughly thesame value. In addition, it is so configured that the gain of the modelestimated lateral jerk and the gain of the lateral jerk based onmeasured values would be roughly the same.

Next, GRAVEL is intended mainly for use when traveling on wet roads ordirt roads, and the control threshold indicated in FIG. 21 is so set asto be slightly high. In addition, although a linear combination mode isadopted, the configuration is such that steerage is improved by havingthe gain of the model estimated lateral jerk be slightly greater thanthe gain of the lateral jerk based on measured values.

Further, SNOW is intended mainly for use when traveling on snow roads,and the control threshold indicated in FIG. 21 is so set as to beslightly high even in comparison to GRAVEL. In addition, select-highcontrol is adopted, and the gain of the model estimated lateral jerk isgreater than the gain of the lateral jerk based on measured values.Thus, steerage and continuity of motion with respect to lateral motionwith a delayed response are ensured.

Changes in vehicle response that accompany changes in road surfaceconditions greatly affect the driver's driving operation, and thevehicle motion itself also varies significantly as a result. It becomesimportant to perform appropriate driving operations with respect tovehicle response that varies from moment to moment. With respect to acontrol system of the present invention, appropriate driving operationsby the driver are assisted by displaying the control state and thevehicle motion state on the multi-information display 82 within thevehicle cabin. As for display modes, there are provided a plurality ofmodes for indicating the present vehicle motion state and displayingreference information to help the driver make driving operationdecisions, such as by indicating a “g-g” diagram where the horizontalaxis represents the vehicle's longitudinal acceleration and the verticalaxis the vehicle's lateral acceleration, or time series data ofacceleration.

Further, the tire braking forces/driving forces, or the generated yawmoment, is/are displayed to make the control state clear, therebyindicating whether the vehicle is currently in a “G-Vectoring controlstate” or a “DYC state.” The aim here is to make the control effect withrespect to the presently generated vehicle motion clear, thereby havingthe vehicle driving operations by the driver be performed moreappropriately. In particular, “G-Vectoring control” emulates“acceleration/deceleration operations coordinated with lateral motion”performed by an expert driver, and does not independently control thebraking forces/driving forces of the four wheels. Accordingly, if thedriver is able to perform comparable acceleration/deceleration drivingoperations, a comparable motion may be attained without any activeinvolvement in the control by the system. It is speculated that byphysically feeling his own driving operations and the vehicle motionsthat accompany them, and, further, seeing the control state on themulti-information display 82, the driver will more likely be able toperform “G-Vectoring control” on his own.

Thus, a control configuration in which acceleration/deceleration that iscoordinated with steering operations and that is active from the normaldriving region is automatically performed, and in which sideslip in thecritical driving region is reliably reduced has been addressed, as wellas solutions for its problems in practice. With the present invention,it becomes possible to provide a technique and system that cause less ofan unnatural feel and enable an improvement in safety performance.

Further, with respect to emergency avoidance, additional notes are madebelow regarding the present invention's superiority in performance overconventional sideslip prevention systems.

With conventional sideslip prevention systems, left and right brakingforces or driving forces would be controlled after sideslip hasoccurred. With respect to emergency avoidance, if the driver were toperform an abrupt steering operation in order to avoid an obstacleahead, thereby causing understeer, the occurrence of understeer wouldfirst be awaited, and left and right braking forces would then beapplied so as to cause a moment that cancels the understeer. In otherwords, between the occurrence of understeer and its being sensed, therewould be a no brake state, and the vehicle would approach the obstacle.In contrast, with the present invention, a braking force is generatedfrom the moment steering is started by the driver, as a result of whichthe speed relative to the obstacle is clearly reduced, thereby enablinga significant improvement in emergency avoidance performance.

Further, by virtue of an improvement in steer response, the absolutevalue of the initial steering angle for performing avoidance becomessmaller, and not as much easing of steering would be necessary afteravoidance. Thus, a stable avoidance operation may be attained withoutvoluntarily causing the vehicle response to become jerky due to steerresponse delay (similar effects may be attained when turning a sharpcurve as well).

1. A vehicle motion control system capable of independently controllinga driving force and braking force of four wheels, the vehicle motioncontrol system comprising: a first mode in which substantially the samedriving force and braking force are generated with respect to left andright wheels among the four wheels based on a target longitudinalacceleration/deceleration control command that is coordinated with alateral motion of the vehicle; and a second mode in which differentdriving forces and braking forces are generated with respect to the leftand right wheels among the four wheels based on a target yaw momentderived from sideslip information of the vehicle, wherein the first modeis selected when the target yaw moment is equal to or less than apre-defined threshold, and the second mode is selected when the targetyaw moment is greater than the threshold.
 2. The vehicle motion controlsystem according to claim 1, further comprising: a vehicle lateralmotion model that estimates estimated lateral acceleration, a target yawrate, and a target sideslip angle based on inputted steering angle δ andvehicle speed V; a first processing unit that calculates the targetlongitudinal acceleration/deceleration control command based on lateralacceleration and lateral jerk that are calculated based on the estimatedlateral acceleration and actual lateral acceleration; a secondprocessing unit that calculates the target yaw moment based on adeviation between the target yaw rate and an inputted actual yaw rate,and on a deviation between the target sideslip angle and an inputtedactual sideslip angle; and a braking force/driving force distributionunit that calculates a braking force/driving force of each wheel of thevehicle based on the target longitudinal acceleration/decelerationcontrol command or on the target yaw moment.
 3. The vehicle motioncontrol system according to claim 2, wherein it is determined whether ornot the target longitudinal acceleration/deceleration control command iszero, and if the target longitudinal acceleration/deceleration controlcommand is not zero and the target yaw moment is equal to or less thanthe pre-defined threshold, a braking force/driving force of each wheelof the vehicle is calculated at the braking force/driving forcedistribution unit based on the target longitudinalacceleration/deceleration control command so as to distribute thebraking forces/driving forces of the left and right wheels substantiallyevenly.
 4. The vehicle motion control system according to claim 2,wherein it is determined whether or not the target longitudinalacceleration/deceleration control command is zero, and if the targetlongitudinal acceleration/deceleration control command is zero, or ifthe target longitudinal acceleration/deceleration control command is notzero and the target yaw moment is greater than the pre-definedthreshold, a braking force/driving force of each wheel of the vehicle iscalculated at the braking force/driving force distribution unit based onthe target yaw moment so as to distribute the braking forces/drivingforces of the left and right wheels individually.
 5. The vehicle motioncontrol system according to claim 1, wherein actual longitudinalacceleration during control in the second mode is correctivelycontrolled in such a manner as to apply substantially the same brakingforce and/or driving force to the left and right wheels among the fourwheels so as to reduce the difference relative to the targetlongitudinal acceleration/deceleration control command.
 6. The vehiclemotion control system according to claim 1, wherein the targetlongitudinal acceleration/deceleration control command is so determinedas to transition in a curved manner in a diagram with the passage oftime, the diagram being defined in such a manner that its horizontalaxis represents the vehicle's longitudinal acceleration and the verticalaxis the vehicle's lateral acceleration.
 7. The vehicle motion controlsystem according to claim 1, wherein the target longitudinalacceleration/deceleration control command is determined in such a mannerthat the vehicle decelerates as the vehicle's lateral accelerationincreases, and that the vehicle accelerates as the vehicle's lateralacceleration decreases.
 8. The vehicle motion control system accordingto claim 1, wherein the target longitudinal acceleration/decelerationcontrol command is determined in such a manner that the vehicledecelerates as the vehicle's steering angle increases, and that thevehicle accelerates as the vehicle's steering angle decreases.
 9. Thevehicle motion control system according to claim 1, wherein the targetlongitudinal acceleration/deceleration control command, G_(xc), isdetermined by $\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 1} \right\rbrack & \; \\{G_{xc} = {{{- {{sgn}\left( {G_{y} \cdot {\overset{.}{G}}_{y}} \right)}}\frac{C_{xy}}{1 + {Ts}}{{\overset{.}{G}}_{y}}} + {G_{x\_ DC}\left( {{\mspace{14mu} {\overset{.}{G}}_{y}} = {G_{y\_}{dot}}} \right)}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$ (where G_(y) is vehicle lateral acceleration, G_(y) _(—)dot is vehicle lateral jerk, C_(xy) is gain, T is a first-order lag timeconstant, s is a Laplace operator, and G_(x) _(—) _(DC) is anacceleration/deceleration command by a driver or that is automaticallyinputted based on external information).
 10. The vehicle motion controlsystem according to claim 1, wherein, where the vehicle's measuredlongitudinal acceleration and lateral acceleration are indicated in adiagram whose horizontal axis represents the vehicle's acceleration inthe positive direction and deceleration in the negative direction, andwhose vertical axis represents the vehicle's leftward lateralacceleration in the positive direction and rightward acceleration in thenegative direction, if the target yaw moment is a clockwise value asviewed from above the vehicle, a greater deceleration force is impartedto the left wheels than the right wheels or a greater driving force isimparted to the right wheels than the left wheels, and if the target yawmoment is an anti-clockwise value as viewed from above the vehicle, agreater deceleration force is imparted to the right wheels than the leftwheels or a greater driving force is imparted to the left wheels thanthe right wheels.
 11. The vehicle motion control system according toclaim 6, wherein, where the vehicle's measured longitudinal accelerationand lateral acceleration are indicated in a diagram whose horizontalaxis represents the vehicle's acceleration in the positive direction anddeceleration in the negative direction, and whose vertical axisrepresents the vehicle's leftward lateral acceleration in the positivedirection and rightward acceleration in the negative direction,longitudinal acceleration/deceleration is determined in accordance withlateral motion in such a manner as to exhibit a clockwise curvedtransition with the passage of time if an anti-clockwise motion isstarted as viewed from above the vehicle, and to exhibit ananti-clockwise curved transition with the passage of time if a clockwisemotion is started as viewed from above the vehicle.
 12. The vehiclemotion control system according to claim 1, wherein the sideslipinformation of the vehicle comprises a steering angle, a vehicle speed,a yaw rate, and a sideslip angle.
 13. The vehicle motion control systemaccording to claim 2, wherein the braking force/driving forcedistribution unit calculates the braking force and/or driving force ofeach wheel of the vehicle based on a deviation between the targetlongitudinal acceleration/deceleration control command and a valueobtained by multiplying measured actual longitudinal acceleration by apre-defined gain or by differentiating the measured actual longitudinalacceleration.
 14. The vehicle motion control system according to claim2, wherein the target longitudinal acceleration/deceleration controlcommand is determined using one of lateral jerk calculated using theestimated lateral acceleration estimated with the vehicle lateral motionmodel and actual lateral jerk obtained by differentiating the vehicle'sactually measured lateral acceleration.
 15. The vehicle motion controlsystem according to claim 2, further comprising: a plurality of modeswith varying calculation methods for the target longitudinalacceleration/deceleration control command; and switching means forswitching between the plurality of modes.
 16. The vehicle motion controlsystem according to claim 15, wherein the plurality of modes are modesof calculation methods for the target longitudinalacceleration/deceleration control command that vary in accordance with atraveled road surface.
 17. The vehicle motion control system accordingto claim 15, wherein the switching means comprises a control selectorthat is provided within the vehicle and that is switchable throughdriver operation.